Low head vibrating screen



Jan. 17, 1939. c. s. LINCOLN ET AL LOW HEAD VIBRATING SCREEN Filed April9, 1956 2 Sheets-Sheet 1 .Fan. 1?, 1939. c. 's. LINCOLN ET'AL 2,144,382

Low HEAD VIBRATING SCREEN Filed April 9, 1936 2 Sheets-Sheet 2 PatentedJan. 17, 1939 LOW HEAD VIBRATING SCREEN Charles S. Lincoln, Wauwatosa,Mathew P. Hahn, Milwaukee, and Roscoe R. Rockafield, West Allis, Wis,assignors to Allis-Chalmers Manufacturing Company, Milwaukee, Wis., acorporation of Delaware Application April 9, 1936, Serial No. 73,450

6 Claims.

This invention relates to a vibrating screen assembly, and particularlyto a vibrating screen adapted for use in a substantially horizontalposition. More particularly the invention comprises a screen body freelyand yieldingly suspended in a substantially horizontal position andhaving a vibrator rigidly attached to the screen body and adapted tovibrate the screen in a. plane at an acute angle to the plane of thescreen 10 body.

An object of this invention is to provide a simple, balanced,self-oiling, rectilinear vibrating mechanism for use in conjunction withvibrating bodies.

15 A further object of this invention is to provide a centrifugal,rectilinear vibrator, the amplitude of vibration of which is adjustableindependently of the frequency thereof.

- The invention is illustrated in the following 2 figures, wherein:

Fig. 1 is a cross-sectional elevation of the screen assembly of thisinvention;

Fig. 2 is a central longitudinal cross-section of the vibratingmechanism taken on the line II-II a of Fig. 3;

Fig. 3 is a transverse sectional view of the vibrating mechanism takenalong the line III-III of Fig. 2;

Figs. 4, 5, 6, and 7 are diagrammatic views of so 318 vibratingmechanism in four successive posions;

Fig. 8 is a central longitudinal sectional view of a modified form ofvibrating mechanism taken along the lines VIII-VIII of Fig. 9; and

3 Fig. 9 is an end view of the vibrating mechanism of Fig. 8 with theclosure plate removed.

It has been the custom in the past to mount vibrating screens at anappreciable angle to the horizontal, in order that thematerialespecially the oversize-may travel along the length of thescreen from the feed end to the discharge end thereof. This method ofmounting the screen is subject to two decided disadvantages. In thefirst place, the inclined position of the screen 45 body requires aconsiderable space, which is seldom conveniently available in plantswhere vibrating screens are used; and secondly, when a screen is mountedat an angle to the horizontal, the force of gravity acting on thematerial in a vertical direction directs the material at an acute angleto the screen surface, so that part of the material, even thoughcomprised of fine particles, is deflected to roll down the screeninstead of passing through it.

Horizontal screens, on the other hand, take up but little space in avertical direction; and gravity actuates the material in a directionperpendicular to the screen surface, so that all of the fine materialcan pass through the screen cloth, instead of rolling along the surface.Horizontal vibrating screens have not been widely used heretoforebecause there has been no satisfactory means for advancing the materialalong the screen, to get a continuous screening action. The applicationof a vibrating 10 force in a plane at an acute angle to the screensurface has made it possible to use a horizontal screen--or even ascreen arranged with its discharge end'higher than its feed end-and yetobtain a positive movement of the material toward the discharge end ofthe screen. This is accomplished by reciprocating the screen in astraight line at an acute angle to the horizontal, the direction ofreciprocation being upward in the direction of movement of -the materialand go downward in the direction of the feed end. While a rectilinearvibrator is illustrated, it is clear that any mechanism which causesvibration of the screen in a plane which makes an acute angle with thescreen would also be efiective.

A vibrator designed for applying this reciprocating rectilinear movementto the screen consists essentially of a casing carrying two parallelshafts geared to rotate in opposite directions at the same speed. Eachshaft is provided with eccentric weights, the distribution of theweights being symmetrical on each shaft to avoid unbalanced couplesbetween the vibrating mechanism and its mounting. The vibrator ispreferably mounted rigidly on the screen body in position to exert itsforce to the screen body at the center of gravity thereof, the vibratorsupports being fixed on the sides of the screen body.

The vibrating screen illustrated comprises a screen body made of framemembers l0 and reinforcing members II, and carries one or more screencloths P2. The screen has a feed hopper l3 and a discharge end It, andthe fines pass through the screen cloth while the oversize passes overthe screen to the discharge end, as is well known to those skilled inthe art. The screen is suspended by four cables l5, which are attachedto an overhead support (which may be part of the building in which thescreen is housed) through helical springs it. These may be eithertension or compression springs.

Mounted rigidly on the screen bodyby means of supports I8 is a vibratorl9 which may be operated by means of a motor 20, mounted on a ustationary support, which actuates the vibrator through elastic belts2|. The vibrator supports iii are fixed on the screen frame members ill,to be in line with the force exerted by the vibrator. An angle of 45between the screen cloth and direction of force exerted by the vibrator,which has been found by test to be the most effective, is shown. Thesupports i8, which serve not only to support the weight of the vibrator,but also serve to transmit the vibrating force to the screen body, arelocated in a plane passing substantially through the center of gravityof the screen body, indicated by the numeral 22, so that all parts ofthe screen frame are reciprocated equally. It will be noted that, whilethe vibrating mechanism l9 reciprocates rapidly with the screen to whichit is rigidly connected, the driving motor is attached to a fixedsupport, and is not exposed tothe' hard wear resulting from rapid.vibration. A particularly effective means of transmitting power fromthe fixed motor to the vibrating sheave 30 is by a plurality of V- beltsof elastic rubber composition, which are known in the transmission artby the trade name Texropes.

The construction of, the vibrator I9 is best shown in Figs. 2 and 3. Thecasing 24, of generally cylindrical form, is provided with end walls and26, which carry parallel shafts 21 and 28 in self-aiming bearings 29.The shaft 21 extends beyond the casing at one end, and carries a sheave30 fixed thereon. Bearing covers 3| and appropriate packing at thepulley end of shaft 21 serve to seal the casing so that it.may containoil for lubricating the bearings 29. Identical gears 33 and 34 arefixedcentrally of shafts 21 and 28, respectively, for mutual engagement,whereby the rotation of sheave '30 serves to rotate shafts 21 and 28 atequal speeds in opposite directions. f

Mounted symmetrically on opposite sides of gear 34 are two eccentricweights or masses 35, fixed on shaft 28. Another pair of eccentricweights 36 are-fixed on shaft 21 symmetrically with respect to gear 33.These weights 35 and 36 are spaced axially on their respective shafts soas not to interfere with each other during operation of the vibrator.rotation of pulley 30 will cause shafts 21 and 28 and their weights torotate at the same speeds in opposite directions. The weights 35 and 36are so fixed on their respective shafts that the resultant of thecentrifugal force caused by their rotation will always be along the lineperpendicular to the plane passing through the axes of the shafts asexplained below.

The particular arrangement of rotating weights shown in Fig. 2 beingsymmetrical about the transverse center of the casing, no twistingcouple results from the rotation of the weights. The operation of thevibrator to produce vrecti linear vibration is best illustrated in Figs.4 to'Z, which show diagrammatically the location of the eccentric weightat four successive positions 90' apart in the rotation of the shaft. -Inthe position of the weight shown in Fig. 4, the centrifugal forces dueto both weights are in the same direction, namely, upward to the right,and the resultant force exerted on the screen will be in this direction,and equal in magnitude to the sum of these two forces.

One-quarter cycle later the weights will be-in the position shown inFig. 5, the centrifugal force acting on each being opposed by the equaland It will be seen that amass:

opposite centrifugal force acting on the other, the net force acting onthe screen being zero.

Fig. 6 shows the position of the weights a half cycle after the positionillustrated in Fig. 4. Here the centrifugal forces acting on bothweights are again exerted in the same direction, but opposite to thedirection in which they act in Fig. 4, thus effecting a return strokefrom the movement caused by the force illustrated in Fig. 4.

After another quarter cycle has elapsed, the weights will be in theposition shown in Fig. 7, where the centrifugal forces acting on theweights again oppose each other, the net force acting on the screenbeing zero.

From the above description, wherein the vibrating mechanism isillustrated in its positions of zero and maximum force in bothdirections,

- it is clear that the vibrator exerts a force which.

varies between zero and two maxima in opposite directions, the forcebeing always directed along the same straight line-hereinafter termedrectilinear force. The magnitude of this force has a sinusoidalvariation.

Fig. 3 shows at 39 the level of the oil contained in the sealed casing.It will be seen that as the shaft 21 rotates, the weights 36 fixedthereto dip into the oil and distribute it, and serve to lubricate allfour bearings. The gear 33 may also dip into the oil.

Since the vibrating mechanism is rigidly mounted on the screen body, themechanism imparts a sinusoidal rectilinear force to the screen body in adirection approximately 45 with the horizontal. Since the screen body isfreely suspended on springs, the movement of the body produces areaction on the part of the springs, tending to return the body to itsposition of rest. Thus the four forces acting on the screen, namely, theforce of gravity, the rectilinear force of the vibrator, the reactiveforce of the springs, and the inertia of the screen body and vibratingmechanism, combine to pifiduce a linear pulsating reciprocation of thescreen.

It will be noted that as the screen moves upward to the right, itcarries its load of material with it. As the-screen slows down andreverses its movement, the material continues its upward and onwardmovement due to its own inertia and then falls back on to the screencloth as the screen begins its upward movement again. The trajectory ofthe material constitutes a parabola which starts with a line at 45 tothe screen cloth, reaches a maximum height, and then falls downward andis suddenly interrupted in its trajectory by impact with the screencloth. This impact tends to expedite the separation of the material intofines and oversize, while the 45 trajectory causes a rapid advance ofthe oversize along the screen to the discharge end.

Because the screen is freely suspended, the reciprocation of the screenis not transmitted to the overhead support. The horizontal position ofthe screen makes for a maximum separating effect on the material beingscreened, and also makes it possible to place the screen in locations'where little head room is available. The vibration at 45 to thehorizontal produces a satisfactorily rapid advance of the material alongthe screen. In fact it has been found in practice that the screen willadvance the material toward the discharge end even when the screen isinclined so that the discharge end is at a higher elevation than thefeed end. In other words the screen will convey material up It has alsobeen found in practice that the screen here disclosed is unexpectedlyeffective in eliminating any clogging. All screens, especially whenusing cloths of large mesh, occasionally become clogged due to pieces ofmaterial becoming wedged in the screen. Possibly due to the rapid andpositive movement of the screen, aided by the forward advance of thematerial being screened, pieces of stone or ore which become clogged orwedged within the meshes of the screen cloth are soon thrown up andcontinue under way. This action is in part due to the suddendeceleration of the screen when, in its upward movement, it receives theimpact of the falling material which had'been thrown upward on thepreceding upward movement of the screen.

If desired, a tension spring 40 may connect the screen body with anadjacent fixed part, in order to provide the necessary tension on thebelt 2!.

A modified form of vibrator, wherein the magnitudeof the resultingrectilinear force is adjustable, is shown in Figs. 8 and 9. In thevibrating mechanism illustrated in Figs. 2 and 3, if it be desired toalter the amplitude of vibration, it is necessary to completelydisassemble the mechanism, and substitute weights of a differentmagnitude for the weights 35 and 36. This is a lengthy and difilculttask, involving some provision for taking care of the oil in the casing,and also necessitating the removal and application of weights on theshafts 35 and 36, these weights being usually shrunk on the shaft forincreased rigidity.

This difficulty is largely obviated when the vibrating mechanism isconstructed in accordance with Figs. 8 and 9. This modification includesa split casing 42, open at both ends, and having a gear case 43centrally thereof, closed by intermediate walls 44. Parallel shafts 21and 28 are rotatably mounted in bearings 29' fixed in walls 44, one ofthe shafts having a sheave 30 thereon. Fixed on shafts 21 and 28 areduplicate gears 33 and 34, respectively, mounted within the gear case43. The gear case may contain oil (not shown) to lubricate the gears andbearings into which one of the gears may dip. Mounted on each end ofeach shaft, adjacent to the gear case, are composite eccentric weights46. Each composite eccentric weight consists of a simple eccentricweight 41 fixed on its shaft, and an adjacent similar eccentric weight48 angularly adjustable on the same shaft. The adjustable weight 48 isprovided with an arcuate slot 50 through which screw 5| is adapted topass. Screw 5| is inserted into a tapped aperture (not shown) in fixedweight 41.

This construction makes it possible, by loosening screw 5|, to moveadjustable weight 48 to any angular position with respect to fixedweight 41, within limits. Such relative movement serves to vary theeccentricity of the composite eccentric weight from a maximum when theangular positions of the fixed and adjustable weights coincide, to aminimum of zero when the fixed and adjustable weights are mounted at anangle of 180 apart. It will be observed that in order to maintain abalanced rectilinear system of forces, all adjustable weights on oneshaft must be moved in the same direction and mounted at the same angle,and the adjustable weights adjustable weights on the other shaft, as is'clearly exemplified in Fig. 9.

. desired angle.

Removable end plates 52 and 53 close the open casing, for greatercleanliness and safety.

When it isdesired'to vary the amplitude of vibration caused by thisvibrating mechanism, it is only necessary'to remove end plates 52 and53,

loosen the screw iii of each weight, move the vibrating mechanism, theweights and gears are symmetrically located on their respective shafts,

so that there is no unbalanced couple tending to twist the vibratingmechanism on its support.

' This is an important feature, since the presence of any such twistingcouple would soon shake the vibrator loose from its support. Thesevibrators and screens receive very hard usage in industry and must bevery rugged and dependable to survive under the rough treatment receivedin rock and ore treating plants, cement mills, mines, etc.

While the vibrator has been shown 'as being applied to a horizontalscreen to reciprocate it at an angle to the horizontal, it can obviouslybe applied to the vibration of screens at any desired angle, or thescreen itself may be mounted at any Moreover, the vibrator may be usedto vibrate apparatus other than screens, such as sieves, hoppers,sifters, tappers, packing and tamping apparatus, etc., and is especiallyap-' plicable to feeders and conveyors of the reciprocated type.

While a specific construction has been described for purposes ofillustration, it is to be understood that the invention is not to bere-'- stricted to the exact details shown and described since variousmodifications within the scope of the claims will-occur to personsskilled in the art to which this invention pertains.

It is claimed and desired to secure by Letters Patent: I

l. A vibrating mechanism comprising a casing having two intermediatewalls forming a gear case, said walls being provided with bearings, twoparallel shafts mounted in said bearings, said shafts being providedwith meshing gears of equal diameter within said gear case, eccentricweights fixed on each shaft at each side and exterior to the gear case,the weights on each shaft being arranged thereon symmetrically of thegear on said shaft, providing a balanced vibrating mechanism.

2. A vibrating mechanism as defined in claim 1 wherein a body of oil iscontained in said gear case, in which at least one of the gears ispartly immersed.

3. A vibrating mechanism comprising a housing, two intermediatewalls'therein forming a gearcase, said walls being provided withbearings, two parallel coextensive shafts mounted in said bearings andcontained within said housing, a gear fixed centrally on each shaftwithin said gear case, said gears being of equal diameters and meshingwith each other, equal eccentric weights fixed on each end of each shaftwithin the housing but exteriorly of said gear case, the center ofgravity of all the weights on each shaft being located in a single planepassing through the axis of said shaft, and the shafts being so relatedthat when the centers of gravityof the weights on one shaft are at oneside of the shaft shafts, the centers of gravity of the weights ontheother shaft are in the same-plane and on the opposite side of said lastnamed shaft.

' 4. A vibrating mechanism comprising a casing having side walls and endwalls, said end walls being provided with bearings, two parallel shaftsmounted in said bearings and extending beyond the end walls at bothends, a gear carried by each shaft between the end walls, said gearsbeing of equal diameters and meshing with each other, masses ofadjustable eccentricity mounted at each end of each shaft exteriorly ofthe end walls, and removable end plates mounted on said side walls forencasing said eccentric masses.

BJM SBB in the plane passing through the axes of the two said shafts.

CHARLES S. LINCOLN.

